によると / によれば

Marks the source of information: "according to X." The statement that follows is reported from that source, so the sentence usually ends with a hearsay expression such as そうだ, らしい or ということだ.

Used in both conversation and writing, and very common in news reports and when passing on information from forecasts, newspapers, surveys or other people. によると and によれば are largely interchangeable. The pattern names the source at the start of the sentence, and a hearsay ending such as そうだ, らしい, ということだ or とのことだ normally closes it.

• 1.
  ということだN3「ということだ」 comes at the end of the sentence, attaches to the plain form, and carries the hearsay content; it often pairs with 「によると」, with each playing a distinct role, so the two cannot be swapped. 「ということだ」 also has a 'in other words' concluding sense.
• 2.
  そうだN4「そうだ」 attaches to the plain form at the end of the sentence to show the content was heard from someone; 「によると」 attaches to a noun and points out the information source. They cannot be swapped and are often used together as 「～によると、～そうだ」; when inferring from data, 「はずだ」 and similar are more common.
• 3.
  らしいN4「によると」 attaches to a noun to state the source; 「らしい」 attaches to the plain form (nouns and な-adjectives attach directly without 「だ」) and, at the end of the sentence, expresses hearsay or conjecture, and can be used on its own. They cannot be swapped; the common pattern is 「…によると、…らしい」.
• 4.
  んだってN3「んだって」 goes at the end of the sentence to mean 'I heard that,' without needing to name a source, and is used only in casual speech; it has no use for inferring from data. In casual chat it can be used with 「によると」, replacing sentence-final 「そうだ」.
• 5.
  に基づいてN2「に基づいて」 expresses the basis for an action or judgment and leans toward written style; 「によると」 introduces the source of information and is followed by hearsay or inference. When the first item is data and the second is an inference, they are sometimes interchangeable, but the emphasis differs.
• 6.
  からすると / からすればN2「からすると」 focuses on making one's own judgment using the preceding item as a clue, and can also mean 'from someone's standpoint'; 「によると」 introduces the source of information, and when reporting hearsay it generally pairs with 「そうだ」 and the like—in that use it cannot be replaced with 「からすると」.

ということだ, そうだ (hearsay), らしい and casual んだって are sentence-final endings that mark information as reported, and they often pair with によると, which names the source at the start of the sentence. に基づいて means "based on" and names the basis for an action or judgment, while からすると / からすれば means "judging from" and introduces the speaker's own inference.